Question

What is the cause of early sunrise and late sunset?

Answer 1

During sunrise, when the sun is just below the horizon, our atmosphere causes the light rays to bend and we see the sun early. Similarly, at sunset, the apparent position of the sun is visible to us and not the actual position due to the same bending of light rays effect.

Answer 2

this is due to atmospheric refraction. Even when the sun is below the horizon in the evening and the morning ,rays of light from the sun below the horizon reach us due to refraction of light.  These rays appear to come from the apparent position of the sun and not from the actual position.Thus we see the sun for a few minutesbefore actual sunrise and few minutes after the actual sunset.